Approximately 200 million throughout the world have chronic hepatitis C viral (HCV) infection. HCV is leading cause of liver cancer and indication for liver transplantation. Enhanced understanding of HCV-host interactions and the mechanisms that regulate immunity within the liver is required to combat this virus and to develop improved therapies. Our laboratory has focused on understanding the role of innate immune cells such as dendritic and natural killer cells, as well as adaptive immunity mediated by CD4+ and CD8+ T cells. Recently our laboratory has become interested in liver sinusoidal endothelial cells (LSECs) which are highly frequent in the liver. Although LSEC-mediated suppression is critical for control of inflammation, it likely compromises protective immunity against HCV infection. Surprisingly little is known about LSECs in HCV infection. We will use a combination of human derived specimens, including LSECs, hepatocytes, and T cells, as well as pharmacologic and silencing strategies in multi-cellular models. In this new application, we will determine the differential effects of HCV sensing by human liver sinusoidal endothelial cells (LSECs) on antiviral IFN signaling. We hypothesize that HCV employs multiple strategies to target LSECs, including direct infection, pinocytosis, or binding of HCV-specific proteins such as core. The uptake of apoptotic HCV-infected hepatocytes or enhancement of an inflammatory state that may regulate the expression of viral or trafficking receptors may ultimately play either protective or adverse roles in HCV dissemination within the liver. In addition, we will characterize the mechanisms that enhance or antagonize LSEC-derived factors' ability to inhibit viral replication in primary and immortalized hepatocytes, the autocrine effects of Type I and III IFNs, and the transcriptional elements that regulate IL-28B (IFN- 3) induction within LSECs. Understanding the multiple ways in which HCV interacts with LSECs to modulate the production of antiviral cytokines such as IFNs, the specific intracellular signaling pathways involved, as well as effects within the hepatic sinusoidal microenvironment will ultimately provide novel mechanistic insights and potential therapeutic targets for this common infection. We will also define the specific processes whereby HCV- experienced LSECs induce a regulatory CD4+ T cell phenotype and impair function of CTLs, identifying mechanisms to reverse this suppression in order to enhance anti-viral immunity. To date, we have found that LSECs upregulate Galectin-9 and reactive oxygen species with HCV core protein. Completion of the aims outlined in this application would ultimately provide a vertical step in the field by linking innate LSEC function to control of adaptive immunity.